A modern furnace runs a strict startup sequence, and knowing where the sequence breaks is most of the diagnosis. The thermostat calls, the inducer motor spins up to prove draft through a pressure switch, the hot surface igniter glows, the gas valve opens, the burners light, the flame sensor confirms fire, and only then does the blower deliver heat to the house. In Vacaville, CA, the failures cluster at predictable points: an oxide-coated flame sensor, a hot surface igniter cracked from years of thermal cycling, a pressure switch that will not close because the inducer is weak or the condensate trap on a high-efficiency model has clogged, or a control board with a burned relay. Each one stops the sequence cold, and each one mimics the others from the hallway.
When the AC quits in summer, see AC Repair.
Warning Signs for Furnace Repair
The sooner you notice these red flags, the easier and cheaper the fix. Watch for these telltale signs:
- Repeated shutdowns just seconds after the burners light
- Air moving through the vents that never gets warm
- Short cycling every few minutes without reaching the setpoint
- A pilot or burner flame that is lazy yellow instead of crisp blue
- Squeals, scrapes, or grinding noises behind the blower door
- Rust streaks, soot, or water around the cabinet or flue
- Booming or banging at light-off from delayed ignition
- Clicking and a glowing igniter with no burner flame
Don't Wait for a Total Failure
What seems like a minor issue today can take out a compressor or heat exchanger tomorrow. At the first hint of a problem, call (707) 210-0197 for a fast inspection.
